1. Field of the Invention
The present invention relates to a backlight device and also to a liquid crystal display device incorporating a backlight device, and particularly to a backlight device in which a lamp as a light source is attached directly to a transformer, and to a liquid crystal display device incorporating such a backlight device.
2. Description of the Related Art
A liquid crystal display (LCD), which is used as a display device for a liquid crystal monitor, a liquid crystal television, or the like, does not emit light by itself, and therefore requires a lighting system, such as a backlight device. Among such backlight devices are an edge light type in which a cold cathode lamp as a light source is disposed at a side of a light conductive plate wherein light emitted from the lamp is introduced into the light conductive plate from the side and exits out from one major surface of the light conductive plate so as to illuminate a light diffusing plate, and a direct illumination type in which a discharge lamp as a light source, such as a cold cathode lamp, is disposed immediately behind a light diffusing plate wherein light emitted from the lamp illuminates directly the light diffusing plate.
A large LCD display for use as a display device in a liquid crystal television requires illumination with high brightness, and therefore employs mainly a direct illumination type back light device provided with a plurality of lamps. In such a direct illumination type backlight device using a plurality of lamps, the output signal from a transformer at which a high voltage is generated by an inverter is applied to the lamps via connectors and lamp cables so as to light the lamps (refer to, for example, Japanese Patent Application Laid-Open No. 2000-47208, FIGS. 1 and 5).
FIG. 14A is a perspective exploded view of an LCD device 200 disclosed in the aforementioned Japanese Patent Application Laid-Open No. 2000-47208. The LCD device 200 of FIG. 14A includes an upper metal frame 201, an LCD panel 202, LCD panel driving circuit boards 218, 219 and 220, a light diffusing sheet 203, a light diffusing plate 204, lamp reflectors 205, a plurality of line-like lamps 206, a plastic molded case 207, a lower metal frame 208, and a high-voltage and high frequency AC generating circuit (inverter circuit) board 209. The inverter circuit board 209 is attached to the back side (bottom side in the figure) of the lower metal frame 208 and the plastic molded case 207.
FIG. 14B is a top plan view of the relevant portion of a backlight device incorporated in the LCD device 200 of FIG. 14A. Referring to FIG. 14B, a plurality of high-voltage transformers 213, dimmer circuits 226, and connectors 216 are mounted on the inverter circuit board 209, first and second lamp cables 214 and 215 are connected respectively to the both ends of each lamp 206, and the second lamp cable 215 has a connector 217, wherein the inverter circuit board 209 and the lamps 206 are electrically connected to each other by connecting the connectors 216 to the respective connectors 217. In the structure described above, the high-voltage generated at the high-voltage transformer 213 of the inverter circuit board 209 is applied to the electrode of the lamp 206 via the connectors 216 and 217 and via the lamp cables 214 and 215, and then the lamp 6 is lighted on.
For assembling the LCD device 200 shown in FIG. 14A/14B, the lamp cables 214 and 215 have to be wired to the lamp 206, and the connector 217 has to be wired to the lamp cable 215. Especially, the LCD device 200 uses the plurality of lamps 206 thus using a corresponding number of connectors 216 and 217, and lamp cables 214 and 215, and therefore the assembly work described above inevitably involves a lot of labor and cost. Further, the connectors 216 and 217, and the lamp cables 214 and 215 are required to withstand high voltage and therefore have to be costly thus pushing up the product cost. Also, since the high-voltage transformer 213 is mounted on the inverter circuit board 209 attached to the back side of the backlight device, it is difficult to reduce the thickness of the backlight device, and at the same time since the lamp 206 and the high-voltage transformer 213 are electrically connected to each other by the connectors 216 and 217, a protection circuit means has to be provided in consideration of poor connection, thus also pushing up the product cost.